Ui is Yui's younger sister, who begins the story as a third-year junior high school student, but later enters Yui's high school the following year in the same class as Azusa. Unlike her older sister, Ui is mature, responsible and handles household chores well, though she still shares a strong relationship with Yui and has a great deal of love and respect for her older sister. Despite being a year younger than Yui, she is nearly identical to her with her hair down and is even once able to fool the club. She possesses some of her sister's musical gift, and has a great talent for playing the guitar—she became capable of playing with the rest of the light music club band after only a few days of practice (Yui was sick, so Ui dressed up as Yui to help the band out). She takes particularly good care of Yui and strives to look after her even at the risk of her own health. Ui is actually considered as the ultimate groupie for her sister's band and supports them with all her heart. She occasionally provides a narrative to the story. She is in the same class as Azusa and hangs out with her sometimes.